The disclosure relates to a calibration system, and more particularly, to calibration systems and calibration methods for automatically eliminating imbalance between two or more signals.
Although the delay for each interface trace is expected to be exactly the same, in the actual circuit, the circuit layout may cause various lengths of delay (or skew) between parallel bus interfaces. For example, dynamic random access memory (DRAM) utilizes parallel buses to transfer data, known as data signals DQ, and data strobe signals, known as DQS. The data strobe signal DQS is utilized to access data carried by the data signal. Unfortunately, as mentioned previously, because of the skew caused by the circuit layouts, the signals transferred through different buses may travel through different paths. There are phase differences between these signals. Because of the phase differences, it is more difficult to utilize the data strobe signal to properly align the data signal DQ and to correctly recover the data from the data signal DQ.
Please refer to FIG. 1, which is a simplified diagram of a DRAM 100 outputting a plurality of signals. As shown in FIG. 1, the DRAM 100 outputs data signals DQ and data strobe signal DQS through parallel buses. As mentioned previously, the phase of each output signal DQ or DQS may be different from the remaining output signals due to various delay elements in each signal path.
A method for compensating the imbalances among the signals (including the DQ and DQS) is to utilize an oscilloscope to detect the phase differences among the signals. Once the phase differences are detected, programmable delays are utilized to delay individual signal such that the signals can be adjusted to have the same phase. Consequently, the data carried by the data signals may be fetched more correctly.
However, the aforementioned method does not sufficiently compensate for the measurement of the phase differences because of its reliance on humans. For example, designers must check the phases of the signals individually in an effort to adjust them.